Modern bagging lines

February 1, 2007
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by Peter Naef

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A bagging line in a production plant is closely tied to the associated production and distribution processes, including the upstream and downstream logistics. This may have an impact on the availability of the entire production plant and must therefore be taken into account in evaluating and designing the line.

To achieve the best possible performance, it is essential that the production management and distribution department cooperate closely in defining the basic concept of such a line.

The bag, as a container for packing foods, offers various benefits. It allows for an attractive presentation of the product, is a significant advertising medium and reflects the quality of the product it contains. In the grain-based food sector, bags are made almost exclusively of paper, woven plastic or textiles. A large number of suitable bag and bag closure types are available, such as stitching with the optional addition of tape-bound closures or a folding device, gluing or sealing. Each method has its specific advantages and disadvantages.

Whatever bag and closure type is chosen, this decision will always have an impact on the entire bagging line and its design. In addition, the bag materials used in fully automatic bagging lines must meet higher quality requirements.

OPERATING RELIABILITY AND AUTOMATION

In the design and specification of a bagging line, it is essential to satisfy the specific plant requirements. But a number of fundamental requirements must always be met by bagging lines in food applications.

Two key requirements are high operating reliability and maximum flexibility. Due to the complexity of a bagging line, the individual components must be of high quality and carefully matched to ensure high operating reliability and maximum availability.

Today, automatic bag attachers and bag transfer and spreading units are normally part of the standard equipment of bagging lines. If the proper bag materials are used, an automatic bag attacher will be capable of processing woven plastic bags as well as the paper bags commonly applied. A bag transfer and spreading unit transfers the bag from the bagging spout and feeds it automatically to the bag closing system.

Both automatic units increase the throughput capacity and reduce the manpower requirement. The units can be integrated either with a single-bag packer or in a bagging carrousel equipped with three, four or six spouts.

ACCURACY AND HYGIENE

Modern bagging lines are characterized by their very high bagging weight accuracy and their top hygienic standard. To achieve accurate and consistent bagging weights, a product feed system operating at a constant capacity is needed in addition to specialist know-how in the design of product storage systems and of bagging bins and their dischargers.

The feed and weighing system selected must be matched to the product in question. Despite optimal electronic weight monitoring and automatic weight correction, it is prudent to install a check scale with an automatic scrap bag ejector between the bagging line and the palletizer or load out point to ensure complete monitoring of the packed bags.

In the food sector, hygiene-related legal requirements are becoming increasingly stringent. They must be satisfied by applying the proper system design and preventing product contamination. In this area, a substractive bagging scale with direct bag filling will significantly reduce the risk of contamination compared to conventional batch bagging scales.

Another advantage of substractive weighing is that every actual filling weight is registered and corrections can be made as required, even with fast bagging cycles.

BAG COMPACTING AND CENTRALIZED CONTROL

New, mechanical compacting systems allow more efficient reduction of the volume of bagged product and give bags a more stable form. At the same time, this reduces the handling volume.

As in other areas, automation and centralized control are becoming increasingly important for minimizing the manpower requirement of bagging lines. A state-of the-art control system will enable an entire bagging line, including the automatic palletizer, to be controlled and monitored from a single touch-screen terminal.

Such control systems are capable of selecting a different bag weight together with the appropriate bag size, or of changing the bag layer pattern created by a palletizer. This is done fully automatically and without manual intervention.

Moreover, these systems allow fast error diagnostics of the entire bagging line, which reduces line downtimes and makes it easier to familiarize new employees with bagging operations.

BALANCED WAREHOUSE LOGISTICS

The performance and cost-effectiveness of a bagging line also depends on the warehousing system applied, which must be matched to the specific needs. Increasingly, the method of direct load out straight from the bagging line is being abandoned. This is due to the high bagging capacity required and because the direct linking of bagging and load out and the increasing number of load out variants with the related downtimes make it a less economical method.

An analysis of the plant-specific requirements is a prerequisite for selecting the adequate warehousing concept, which must also consider the plant’s uptime and therefore its profitability.

A number of warehouse variants are possible, which all have their specific advantages and disadvantages. Today, many plants apply the block storage method due to its low capital cost. But it also has the following drawbacks:

• the first-in, first-out (FIFO) approach is not possible;

• a large surface area is needed, with poor space utilization;

• automatic inventory control is not possible;

• the storage and retrieval capacity is low;

• the number of possible variants or items is low.

In addition, the manpower costs of a block storage system are very high, since several forklift drivers are needed simultaneously. The drawbacks of rack storage systems are similar to those of block storage installations, though they do allow FIFO operation to some extent. They also permit order-picking, thanks to the access they allow to individual items in combination with flow-rack or high-bay storage systems.

For many packing installations, a flow-rack store will be an adequate solution. Flow-rack storage systems offer the following advantages:

• FIFO is possible;

• the space utilization rate is high;

• the capacity and uptime are high;

• the manpower requirement is low;

• the capital cost is relatively low, with an excellent price-to-performance ratio;

• supply readiness is optimal.

Fully automated, high-bay warehouses are the highest quality option in the field of warehousing. But despite their outstanding advantages, they are too expensive and complex for many plants. A high-bay storage system is especially suitable if a large number of items must be stored and access to each individual item must be possible at any time.

Peter Naef, a research and development coach in the Bühler AG grain processing division, can be reached at peter.naef@buhlergroup.com. Bühler is a global technology group and a system partner for the supply of plant, equipment, and process know-how to the food processing industries. Buhler has been supplying complete food processing plants for over 100 years and bagging lines in all capacity ranges for more than 40 years, especially for meeting the stringent standards of the food processing industry.